Dimerization process

Abstract

Process for the dimerisation of acrylonitrile (ACN) to predominantly linear C6 dimers using organic phosphinites or phosphonites as catalyst in the presence of a proton-donating solvent and, optionally, a hydrocarbon co-solvent, the ACN and solvent(s) being substantially dry, and a small amount of a compound of a metal of Group IVA to VIIA, VIII or IB to VB being added to the reaction mixture to reduce the amount of polymeric by-product.

What we claim is: 
     
       1. A process for the dimerisation of acrylonitrile to predominantly 1,4-dicyanobutenes, in which the acrylonitrile is contacted with an organic phosphorus (III) compound having the formula ##STR3## where R 1  is a hydrocarbyl group, R 2  is an alkoxy or cycloalkoxy group, R 3  is a hydrocarbyl, alkoxy or cycloalkoxy group and R 4  is a divalent hydrocarbyl or hydrocarbyloxy group, each hydrocarbyl or hydrocarbyloxy group having from 1 to 10 carbon atoms and being unsubstituted or substituted by halogen, cyanide or alkyl groups, at a temperature from 0° to 120° C., the acrylonitrile being dissolved in an organic solvent capable of donating protons, optionally with an inert non-hydroxylic co-solvent, the concentrations of acrylonitrole and said phosphorus (III) compound being in the ranges 5 to 75% and 0.01 to 5% by volume, respectively, and the acrylonitrile and solvent or solvents being substantially dry, characterised in that a polymeric by-product reducing amount of an anhydrous metal compound capable of reducing the proportion of polymeric by-products is added to the reaction mixture, the metal being selected from Group IVA to VIIA, VIII and IB to VB of the Periodic Table of Elements. 
     
     
       2. A process as claimed in claim 1, in which the concentration of the metal compound in the reaction mixture is between 5 and 1000 ppm. 
     
     
       3. A process as claimed in claim 1 in which the concentration of metal compound is from 0.5 to 5% of the concentration of phosphorus (III) compound. 
     
     
       4. A process as claimed in claim 1 in which the metal compound is a co-ordination complex. 
     
     
       5. A process as claimed in claim 1 in which the metal compound is a halide, a sulphate or a carboxylate. 
     
     
       6. A process as claimed in claim 4 in which the metal compound is an acetylacetonate of zinc, nickel, aluminium or gallium. 
     
     
       7. A process as claimed in claim 5 in which the metal compound is zinc, nickel or cobalt dichloride. 
     
     
       8. A process as claimed in claim 1 in which the metal compound is added to the reaction mixture before it is contacted with the phosphorus (III) compound.